The present invention relates to a noise reduction technique for a semiconductor integrated circuit and more specifically to a technique which may be effectively adapted to a semiconductor integrated circuit device comprising an analog section and a digital section for common use of signal input pin for test and signal input/output pin for usual operation, for example, to a technique which may be effectively used for LSI (Large Scale Integrated circuit) which is used in a hand-held telephone set for radio communication to process the transmitting and receiving signals.
There has been proposed a technique to reduce the number of pins through common use of the signal input/output pin for test and the signal input/output pin for usual operation in a semiconductor integrated circuit mounting a test circuit. Moreover, in recent years, an LSI comprising the analog and digital sections, in which an analog circuit and a digital circuit are mounted on the same semiconductor chip, has also be proposed in response to further improvement in packing density of LSI.
In such LSI comprising the analog and digital circuits, when it is required to use in common the signal input/output pin for test and the signal input/output pin for usual operation, the input/output pin for test corresponding to the test circuit of the digital section and the input/output pin for test corresponding to the test circuit of analog section have been provided individually in order to prevent deterioration of accuracy due to the leak of noise to the analog section from the test circuit of digital section because the analog circuit requires higher accuracy. Namely, it has been avoided to use in common the input/output pin for test corresponding to the test circuit of the digital section and the input/output pin for usual operation of the analog section.
However, when the number of pins required for usual operation increases corresponding to progress in the packing density of LSI, it has been required to use the input/output pin for usual operation of the analog section as the input/output pin for test corresponding to the test circuit because of necessity of reduction in size of package through reduction in the total number of pins.
Therefore, the inventors of the present invention have investigated to use in common the input/output pin for test corresponding to the test circuit of digital section and the input/output pin for usual operation of the analog section. At the beginning, the inventors have thought, on the occasion of using the pin usually used as the input/output of the analog section as the input/output pin for test corresponding to the test circuit of the digital section, there is no influence on the analog section from the digital section, if the test circuit is turned OFF in the usual operation mode because there is no exchange of signals between the analog input/output terminal and digital section.
However, as a result of detail investigations, it has been found that if the test circuit is turned OFF in the usual operation mode, a noise generated in the digital section is transferred through the signal path up to the analog input/output pin connected with the test circuit from the test circuit of digital section, resulting in adverse effect on the analog circuit.
It is therefore an object of the present invention to eliminate adverse effect of noise, on a semiconductor integrated circuit comprising the analog and digital sections, that is generated in the digital section and transferred to the analog circuit through the signal path extended from the test circuit of digital section up to the analog input/output pin connected with such test circuit even in the case that the input/output pin for test corresponding to the test circuit of digital section is also used in common as the input/output pin for usual operation of the analog section.
The aforementioned and the other objects and features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
Typical inventions among the inventions disclosed in this specification are briefly explained as follows.
Namely, in a semiconductor integrated circuit of the structure that the analog circuit and digital circuit are formed on one semiconductor substrate and the external terminal of the analog circuit is used in common as the external terminal of the digital circuit, selection switches are respectively provided in the course of the wiring connecting between the external terminal and the analog circuit and the wiring connecting between the external terminal and the digital circuit and a voltage fixing means, for fixing the relevant wiring to the predetermined voltage under the condition that the relevant selection switch is shut off, is connected in the side nearer to the digital circuit than the selection switch of the wiring connecting between the external terminal and the digital circuit.
According to the means explained above, when the external terminal for common use is connected to the analog circuit, the wiring disconnected from the digital circuit and is connected between the external terminal and the digital circuit is fixed to the predetermined voltage. Therefore, noise generated in the digital circuit and noise leaked to the wiring from the peripheral circuits thereof are absorbed. Thereby, even when the external terminal is used in common with the analog circuit and digital circuit, transfer of noise to the analog circuit from the digital circuit can be prevented.
Moreover, a voltage fixing means for fixing the relevant wiring to the predetermined voltage under the condition that the relevant selection switch is shut off is connected respectively to the side nearer to the digital circuit than the selection switch of the wiring connecting between the external terminal and the digital circuit and to the side nearer to the selection switch. Thereby, if the external terminal is isolated from the digital circuit and thereby the wiring connected these elements becomes longer, the voltage of wiring can be fixed respectively at both ends of wiring with the voltage fixing means and accordingly the noise generated in the digital circuit and noise leaked to the wiring from the peripheral area can be absorbed effectively and thereby influence of noise on the analog circuit can be lowered.
Moreover, there is provided a structure that the terminal and wiring for supplying the power source voltage to both analog circuit and digital circuit are formed individually, the voltage fixing means nearer to the digital circuit is capable of fixing the voltage of wiring to the power source voltage of the digital circuit and the voltage fixing means nearer to the selection switch is capable of fixing the voltage of wiring to the power source voltage of the analog circuit. Thereby, it can be prevented that the analog circuit is influenced with the power supply noise of the digital circuit through the analog circuit and that noise generated with operation of the digital circuit is transferred to the analog circuit through the wiring connecting between the external terminal and the digital circuit and the power supply line of the analog circuit.
In addition, a semiconductor substrate explained above is preferably formed of a multilayer structure in which a semiconductor layer is formed on a supporting substrate via an insulation layer and elements forming the analog circuit and the element forming the digital circuit are surrounded preferably with a dielectric insulation band formed to reach the insulation layer through the semiconductor layer. Thereby, noise generated between elements forming the circuit can be lowered.
Moreover, the wiring connecting between the selection switch and the digital circuit among those connecting the external terminals and digital circuit is preferably formed at the upper part of the semiconductor region sandwiched between two insulated separation bands formed up to the insulation layer through the semiconductor layer. Thereby, amount of noise appearing on the wiring connecting the external terminals of common use and the digital circuit resulting from the peripheral circuits of this wiring can be reduced.
Moreover, the voltage fixing means is formed on the surface of the semiconductor region sandwiched between two insulated separation band in which the wiring connecting between the selection switch and digital circuit is formed. Thereby, amount of noise appearing on the voltage fixing means and resulting from the peripheral circuits can be reduced and as a result, noise to be transferred to the analog circuit can also be reduced.
In addition, the external terminal of the analog circuit is structured for common use as the terminal for inputting and outputting the signals of the test circuit of the digital circuit. Since the test circuit of the digital circuit is not operated during the usual operation of the analog circuit, the terminals can be used in common and any influence is applied to the usual operation because it is not required to select the terminals for usual operation.
Moreover, the other invention of the present specification is a semiconductor integrated circuit for processing various signals comprising an oscillation control circuit for generating a control voltages of a first oscillation circuit for generating a first oscillation signal and of a second oscillation circuit for generating a second oscillation signal, an amplifying circuit for amplifying a receiving signal, a first mixer circuit for combining the amplified signal and the first oscillation signal to convert the frequency, a receiving analog circuit including a demodulation circuit for demodulating the signal frequency-converted in the first mixer circuit, a modulation circuit for modulating a transmitting signal, a transmitting analog circuit including a second mixer circuit for combining the modulated signal and the second oscillation signal to convert the frequency, a control digital circuit for controlling the receiving analog circuit and transmitting analog circuit and a test circuit for outputting a signal from the control digital circuit, whereby at least an external terminal for inputting an analog input signal to the transmitting analog circuit or outputting an analog output signal from the transmitting analog circuit is used in common as the external terminal for outputting the signal from the test circuit, the selection switches are respectively provided in the course of the wiring connecting the external terminal and analog circuit and the wiring connecting the external terminal and digital circuit, and a voltage fixing means for fixing the relevant wiring to the predetermined voltage under the condition that the relevant selection switch is in the shut-off condition is connected in the side nearer to the digital circuit than the selection switch of the wiring connecting the external terminal and digital circuit.
According to the means explained above, since the wiring disconnected from the test circuit of the control digital circuit and connected between the external terminal and test circuit of digital circuit is fixed to the predetermined voltage when the external terminal of common use is connected to the transmitting analog circuit, the noise generated in the digital circuit and noise appearing on the wiring from the peripheral circuits of wiring are absorbed and thereby even if the external terminal is used in common with the transmitting analog circuit and test circuit of the control digital circuit, transfer of noise to the transmitting analog circuit from the test circuit of the digital circuit can be prevented.